This application, the Feasibility Study, proposes the following feasibility assessment and preparatory work for the 23-year follow-up (main) study. Specifically, we propose to: Feasibility Aims: 1) Locate and contact 830 respondents of the original study who were interviewed in 1974. This sample includes 263 Vietnam veteran general- sample respondents negative for urinalysis in 1971, 308 vietnam veteran drug-positives in 1971, and 259 civilian controls matched with general- sample veterans. 2) Provide detailed documentation on the tracing procedures used in the feasibility study. 3) Provide cost estimates for the main study from the location rates stratified by risk statuses with different hypothetical methods of ascertainment. Data Analyses: 4) Link the 1972 and 1974 database of the original study with the tracing data obtained in Aim 1. The tracing data include mortality and location outcomes, and contact efforts and procedures for all 830 subjects, as well as current and past medical records and records concerning living situations among veterans traced by the St. Louis Veterans Administration (VA). From the linked database in Aim 4: 5) Estimate whether any biases will exist in the main study. 6) Finalize the sampling strategy for the main study. 7) Examine demographic and behavioral correlates of mortality and geographical mobility of all located subjects. 8) Examine: a) medical utilization patterns of located subjects through VA hospitals' medical records and b) additional outcome measures of located subjects through other VA programs' records. 9) Assess demographic and behavioral correlates of contact efforts and different tracing procedures.